The present invention relates to a direct drawing device for drawing a predetermined pattern on a photoresist layer on a printed circuit board by scanning it directly with an electron beam.
A substrate patterning technique has been used in manufacturing semiconductor devices or printed circuit boards in which an art work film bearing thereon a predetermined pattern is put on a photoresist layer formed on the semiconductor substrate or the printed circuit board, which is sensitive to ultra-violet rays, and exposed to ultra-violet rays and a copper foil pattern, i.e., bare board, is formed after developing and etching thereof. The art work film is usually prepared by a drawing machine called a photo plotter or laser plotter. A drawing pattern data which is given by a computer aided printed circuit board design is supplied to the plotter in which it is converted into a data of a suitable format which is referred to as "Gerber Format" which is composed of a code corresponding to a line width of a pattern and a code assigning a start point cordinate (Xs, Ys) and an end point coordinate (Xe, Ye) of each line segment thereof and a code showing whether or not these line segments are to be exposed and represents a group of patterns over a large circuit board area such as 340 mm.times.400 mm or 500 mm.times.600 mm.
Recently, in order to eliminate the necessity of preparation of the art work film and to reduce a manufacturing cost and time as well as to match with a requirement of production of various semiconductor devices or printed circuit boards each small in number, an electron beam direct exposing system has been developed, in which a predetermined pattern is drawn on a semiconductor wafer or a mask plate by scanning it with an electron beam. In order to make such a direct exposing system usable with the conventional plotter, it is desired that the direct exposing system is responsible to the computer aided design (CAD) output pattern information of the Gerber Format and able to convert it into a suitable format to the system.
In the direct exposing system, when a large area is to be drawn by scanning it with the electron beam while the area is kept stationary, a peripheral portion of the field is irradiated with the electron beam at a small incident angle causing positions of exposition at upper and lower surfaces of the phoresist layer to be different, resulting in a degradation of positional accuracy of a resultant pattern. In order to solve this problem, it is considered to make a work distance between the circuit board and a deflector large enough to obtain a sufficiently large incident angle of electron beam. In this case, however, it becomes difficult to condense the electron beam and the latter may be scattered by residual gas and thus influenced by residual magnetism due to a long beam path. Therefore, the area to be scanned by electron beam should be limited to, for example, 100 mm.times.100 mm which can be scanned by a main deflector, i.e., main deflection regions (referred to as "field", hereinafter), and the respective fields are drawn by the so-called "step and repeat" system one by one by relatively moving the field with respect to electron beam. Therefore, it is necessary that a pattern data over the whole area is divided every field and then edited again. It has been usual to divide a region which can be covered by an electron beam deflected by a main deflector into a plurality of sub-deflection regions (referred to as "sub-field", hereinafter) each covered by a sub-deflector and to shift electron beam from one sub-field to another by the main deflector every time a drawing for the one sub-field completes to thereby complete a drawing of the whole field.
This system is disclosed in, for example, Japanese Patent Application Laid-open No. 244024/1985 and FIG. 4 of the present application shows a portion of a conventional electron beam exposing device having a two-step deflector disclosed therein.
In FIG. 5, electron beam 1 is directed through a blanker 2, an aperture 3, a sub-deflector 4 and a main deflector 5 to a material 6 such as a semiconductor wafer or a mask plate thereon. A region of the material 6 surrounded by a solid line is a field and regions thereof surrounded by dotted lines are sub-fields. A control circuit for controlling the electrooptical system mentioned above is also shown in block in FIG. 4 in which a computer 7 is connected through a drawing data memory 8, a pattern decomposer circuit 9, a sub-deflection correcting circuit 10 for correcting distorsion of sub-deflection, a dot decomposer circuit 11 for a small region and a sub-deflection digital/analog converter (DAC) 12 to the sub-deflector 4 and through a correction coefficient calculator circuit 13 and a main deflector DAC 14 to the main deflector 5. The sub-deflection correction circuit 10 is connected to the correction coefficient calculation circuit 13 and through a blanking amplifier 15 to the blanker 2.
FIG. 6 illustrates an example of drawing operation to be performed by the conventional electron beam exposing device. A left side portion of FIG. 6 shows the material 6 and a right side portion thereof shows one (22) of the sub-fields in the field 21 in enlarged scale. A pattern 23 in the sub-field 22, such as trapezoidal pattern, is divided into seven small regions (paint-out fields). One (24) of the paint-out fields is painted out digitally in dot by point electron beam 1.
In operation, a deflection of electron beam 1 from one sub-field to another is performed by the main deflector 5 and a deflection thereof within each sub-field is performed by the sub-deflector 4. The computer 7 supplies a drawing data to the drawing data memory 8 and a deflection distortion data to the correction coefficient calculator circuit 13. One of outputs of the calculator circuit 13, which assigns a center of the sub-field in the field after correction of its deflection distortion, is supplied to the main deflector DAC 14. The pattern decomposition circuit 9 divides the pattern in the sub-field into the paint-out regions on the basis of the pattern data received from the drawing data memory 8. The sub-deflection correcting circuit 10 receives another output of the correction coefficient calculator circuit 13 which is a deflection correcting coefficient for each sub-field and performs a distortion correction according thereto, a resultant corrected sub-deflection signal being supplied to the dot decomposer circuit 11 in which each paint-out field is decomposed to dots which are supplied to the sub-deflection DAC 12.
The blanking amplifier 15 responds to the output of the sub-deflection correcting circuit 10 to perform a blanking operation at both a start point and an end point of the paint-out field so that electron beam 1 is on-off controlled thereby.
The drawing data memory 8 stores pattern informations of the respective sub-fields of the field which are prepared by the computer 7 by dividing the field.
As mentioned previously, this proposal requires the division of the pattern data of the large area into those of the fields and the re-edition thereof and additionally the division of pattern data of each field into those of the sub-fields and the re-edition thereof. When these operations are to be performed by a computer, the amount of software necessary to the divisions and the re-editions becomes considerable and the amounts of data and processing time become also considerable, respectively. When it should be performed by a hardware, it is necessary to provide, a circuit for automatically dividing the field pattern data to the respective sub-field pattern data. Thus, in either case, the processing of the data becomes complicated and time consuming. Further, unlike the wafer or mask pattern for semiconductor device, it is usual that the pattern of printed circuit board does not include identical pattern portions occuring repeatedly. Therefore, it is impossible to simplify the data processing by using features of such repeatedly occurring identical pattern portions.